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  • Re: Aerodynamic modifications

    Originally posted by Curt_B View Post
    Or, for those that are positive thinkers, 'hi drag".

    Posting the other two videos to make it easier on everyone;

    Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.


    http://www.youtube.com/watch?v=uewkm_pKXOc
    Actually there is a small step above the rear window that causes the airflow to "trip" and dump onto the rear spoiler. They also changed the angle of the window and raised the trunk lid. This change lowered the c/d by a pretty large amount between the normal version and the version I have. . I think the drag dropped from .38 to .33 with that change alone. Watching the water droplets on the hood as I drove through fog this morning I noticed that it splits right down the center of the hood, the airflow doesn't just go straight back to the windshield, it splits and pushes off to the side starting about dead center of the hood and fanning to the sides. I couldn't tell you why it splits there.

    Will

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    • Re: Aerodynamic modifications

      Originally posted by RAD2LTR View Post
      Actually there is a small step above the rear window that causes the airflow to "trip" and dump onto the rear spoiler. They also changed the angle of the window and raised the trunk lid. This change lowered the c/d by a pretty large amount between the normal version and the version I have. . I think the drag dropped from .38 to .33 with that change alone. Watching the water droplets on the hood as I drove through fog this morning I noticed that it splits right down the center of the hood, the airflow doesn't just go straight back to the windshield, it splits and pushes off to the side starting about dead center of the hood and fanning to the sides. I couldn't tell you why it splits there.

      Will
      Pretty cool stuff. There's stagnation, or positive pressure, at the base of the windshield. The air senses that a and decides it's easier to go around. Car aerodynamics are a whole different ballgame.

      Hoping this is acceptable protocol, but some of the photos tell good aerodynamic stories and I've cropped some for the scientific value. While these are other's photos, the aesthetic value has been removed, so tell me if I'm crossing bounds.

      Here's an example series depicting the vortex coming off of Strega's strake, what that looks like in oil flow, both in-flight and on the ground after a flaps-down landing cycle, and a clean Stiletto to encourage those that notice oil/dirt/exhaust/steam in their photos to post.

      Vortex;

      Click image for larger version

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      Side view oil flow in-flight;

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      Bottom in-flight oil flow;

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      Ground;

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      And Stiletto in-flight;

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      Last edited by Curt_B; 10-28-2013, 10:28 AM.

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      • Re: Aerodynamic modifications

        Originally posted by Curt_B View Post
        Pretty cool stuff. There's stagnation, or positive pressure, at the base of the windshield. The air senses that a and decides it's easier to go around. Car aerodynamics are a whole different ballgame.

        Hoping this is acceptable protocol, but some of the photos tell good aerodynamic stories and I've cropped some for the scientific value. While these are other's photos, the aesthetic value has been removed, so tell me if I'm crossing bounds.

        Here's an example series depicting the vortex coming off of Strega's strake, what that looks like in oil flow, both in-flight and on the ground after a flaps-down landing cycle, and a clean Stiletto to encourage those that notice oil/dirt/exhaust/steam in their photos to post.

        Its that stagnation that prompted that cool little "cowl induction" flap on the hood scoop of the 1970 Chevelle Super Sport....

        .....asthetic value is subjective.....these are pretty asthetically pleasing to me. Great stuff guys keep it up, facinating!
        Fledgling Air Race and P-51 Junkie

        Comment


        • Re: Aerodynamic modifications

          Originally posted by Curt_B View Post
          Pretty cool stuff. There's stagnation, or positive pressure, at the base of the windshield. The air senses that a and decides it's easier to go around. Car aerodynamics are a whole different ballgame.

          Hoping this is acceptable protocol, but some of the photos tell good aerodynamic stories and I've cropped some for the scientific value. While these are other's photos, the aesthetic value has been removed, so tell me if I'm crossing bounds.

          Here's an example series depicting the vortex coming off of Strega's strake, what that looks like in oil flow, both in-flight and on the ground after a flaps-down landing cycle, and a clean Stiletto to encourage those that notice oil/dirt/exhaust/steam in their photos to post.

          Vortex;

          [ATTACH=CONFIG]20361[/ATTACH]

          Side view oil flow in-flight;

          [ATTACH=CONFIG]20362[/ATTACH]

          Bottom in-flight oil flow;

          [ATTACH=CONFIG]20363[/ATTACH]

          Ground;

          [ATTACH=CONFIG]20364[/ATTACH]

          And Stiletto in-flight;

          [ATTACH=CONFIG]20365[/ATTACH]
          ...very nice... I have a distinct memory of Stiletto(during the 1986 sunday Gold race) trailing that oil, and knowing the gig was going to be up for Skip Holm in a lap or two. It was exciting while it lasted though.

          If you have not seen this, it is informative on the XP-51 dive tests:http://www.youtube.com/watch?v=mU6i0Ix5QvI

          Comment


          • Re: Aerodynamic modifications

            Originally posted by xmh53wrench View Post
            Its that stagnation that prompted that cool little "cowl induction" flap on the hood scoop of the 1970 Chevelle Super Sport....

            ... and why NASCAR racers with full bodies and windshields have their engine intake at the base of the windshield to this day. That's really a fantastic place to pick up high pressure air on a car. A lot of 60s cars had cable-actuated vents for passenger cabin air that were fed from the grille at the base of the windshield, and it will blow you into the back seat. The Cowl Induction system was one of only a few factory hood scoop designs of the 60s and 70s that gave a pressure rise in addition to cool air.

            There was also a popular car - with the word "Mach" in its name, no less :-) that had a beautifully styled, aggressive-looking hood scoop which was later proven to be right in a LOW pressure area and was doing more harm than good at speed (although it did provide cool air). In fact, a conventional forward-pointing hood scoop on a car usually has to be disproportionately large and ugly in order to actually produce a pressure rise at the engine air intake.

            Comment


            • Re: Aerodynamic modifications

              Here is a perfect display of what I've noticed watching rain on my personal car in terms of where the airflow is going.


              Yes, this was one of the BMW Team cars, but the street cars were identical except they had an interior, the bodywork was the same due to the rules to race.

              Back to P51s racing, those pics of the oil are interesting. The one of Stiletto is pretty cool. Am I correct in thinking the airflow was really smooth based on the fact that the oil trail is fairly straight and even?

              Will

              Comment


              • Re: Aerodynamic modifications

                Originally posted by RAD2LTR View Post
                Here is a perfect display of what I've noticed watching rain on my personal car in terms of where the airflow is going.


                Yes, this was one of the BMW Team cars, but the street cars were identical except they had an interior, the bodywork was the same due to the rules to race.

                Will
                Interesting... it sure LOOKS like a) its a separation area where there would be a lot of turbulence and wasted energy, and b) no air flows cleanly under the rear spoiler, which would seem to render the rear spoiler useless. But again that's intuition based on only one smoke trace that's rather far above the surface of the vehicle.

                Comment


                • Re: Aerodynamic modifications

                  Originally posted by RAD2LTR View Post
                  Back to P51s racing, those pics of the oil are interesting. The one of Stiletto is pretty cool. Am I correct in thinking the airflow was really smooth based on the fact that the oil trail is fairly straight and even?

                  Will
                  Oil flows are like reading X-rays. To the novice, you can see whether the flow is attached or not. For the racers, that's only a first order effect required to compete. To gain the edge, you want to achieve better pressure recovery on the back end than the other guy. In Strega's case, the focused vortices from the strake scrub the boundary off and pump air to the fuselage afterbody, reducing the drag. Stiletto has vortices too, only they're weaker and less well defined. Strega's strake is inclined and produces a strake drag, or device drag, that is overcome by the vortex effect on the fuselage afterbody. The improved case would be to eliminate the device drag and is something that can be done.
                  Last edited by Curt_B; 10-29-2013, 12:11 PM.

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                  • Re: Aerodynamic modifications

                    Originally posted by John View Post
                    If you have not seen this, it is informative on the XP-51 dive tests:http://www.youtube.com/watch?v=mU6i0Ix5QvI
                    Nice video. The data is applicable to the clipped Mustang by allowing for the reduced CL-alpha slope. This has the effect of causing the drag rise to begin at lower Mach numbers.

                    As an aside, always loved the battered lacquer finishes of the period. If I had a Mustang it'd look like that. Though I did cave in and paint my Yak just to stop people from asking when I was going to paint it. Now they say, 'nice paint job', instead of, 'it's a Yak.' Lol.
                    Last edited by Curt_B; 10-29-2013, 12:16 PM.

                    Comment


                    • Re: Aerodynamic modifications

                      Originally posted by RAD2LTR View Post
                      Here is a perfect display of what I've noticed watching rain on my personal car in terms of where the airflow is going.


                      Yes, this was one of the BMW Team cars, but the street cars were identical except they had an interior, the bodywork was the same due to the rules to race.

                      Back to P51s racing, those pics of the oil are interesting. The one of Stiletto is pretty cool. Am I correct in thinking the airflow was really smooth based on the fact that the oil trail is fairly straight and even?

                      Will
                      I am pretty sure i have a pic of that very car in its natural element... the race track, I am pretty sure it is the car that was owned by a guy here in Dunedin NZ for a few years.. looked great, sounded great, and with a decent driver.. went like a cut cat
                      race fan, photographer with more cameras than a camera store

                      Comment


                      • Re: Aerodynamic modifications

                        I have another question about aerodynamic modifications, forgive me if this was covered already, but what is the most efficient shape for a turtle deck? I remember Tiger Destefani saying that Strega's was because of how it flows into the verical stab. but I've also heard that Dago's was actually more efficient because of how it intersected the fuselage at an angle... Can anyone elaborate on this?

                        Comment


                        • Re: Aerodynamic modifications

                          Originally posted by CJAM427 View Post
                          I have another question about aerodynamic modifications, forgive me if this was covered already, but what is the most efficient shape for a turtle deck? I remember Tiger Destefani saying that Strega's was because of how it flows into the verical stab. but I've also heard that Dago's was actually more efficient because of how it intersected the fuselage at an angle... Can anyone elaborate on this?
                          Dago's turtle deck minimizes boundary growth relative to Strega and Voodoo. The sharp fuselage/turtle deck intersection on Strega and Voodoo gets filled in with low energy air. The air gets thicker and thicker as you move toward the tail and gets dumped on the vertical stab/dorsal at the root. The effect is less of a pressure recovery on the aft fuselage/turtle deck and the base of the vert/dorsal and increases drag. Dago's blends into the fuselage and minimizes adverse boundary layer between the turtle deck and fuselage. Dago's starts out with a sharp intersection in the canopy area and quickly geometrically dissipates.

                          Rounding that sharp intersection at the start would improve Dago's a little. Had an ole timey aero guy tell me when I started out that there are no discontinuities in nature when I tried to fair a kinky curve. Whenever I see sharp stuff, it raises a flag.

                          Good eye. Wish we could get some more flow picture details from the stellar photographers in the group.

                          Curt
                          Last edited by Curt_B; 11-05-2013, 04:57 PM.

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                          • Re: Aerodynamic modifications

                            Originally posted by Curt_B View Post
                            Dago's turtle deck minimizes boundary growth relative to Strega and Voodoo. The sharp fuselage/turtle deck intersection on Strega and Voodoo gets filled in with low energy air. The air gets thicker and thicker as you move toward the tail and gets dumped on the vertical stab/dorsal at the root. The effect is less of a pressure recovery on the aft fuselage/turtle deck and the base of the vert/dorsal and increases drag. Dago's blends into the fuselage and minimizes adverse boundary layer between the turtle deck and fuselage. Dago's starts out with a sharp intersection in the canopy area and quickly geometrically dissipates.

                            Rounding that sharp intersection at the start would improve Dago's a little. Had an ole timey aero guy tell me when I started out that there are no discontinuities in nature when I tried to fair a kinky curve. Whenever I see sharp stuff, it raises a flag.

                            Good eye. Wish we could get some more flow picture details from the stellar photographers in the group.

                            Curt

                            Thanks Curt!

                            So where does Precious Metal's deck rank? Since it intersects at a more round angle...

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                            • Re: Aerodynamic modifications

                              Originally posted by CJAM427 View Post
                              Thanks Curt!

                              So where does Precious Metal's deck rank? Since it intersects at a more round angle...
                              There're a lot of shape, line, and contour changes on PM's. Maybe comparable to Voodoo/Strega dragwise. PM's windshield/canopy interface is sealed, which is a good thing. Voodoo/Strega is an unnecessary boundary layer growth deal, PM's is a fluctuating pressure gradient deal due to the shape changes toying with the pressure drag since PM had compromised schedule/design requirements to host a camera. Strega's new canopy/windshield interface with the forward and aft facing, chamfered(?), step right at the minimum pressure location is undesirable at 500mph. Also, Strega's new canopy seems to transition to the turtle deck at an angle on the side view, which is less desirable than a nice straight line if that's what it had before. Considering the circumstances though, it's a mighty fine job.

                              Observation. Not trying to piss anybody off, lol, though I have done that before - inadvertently of course - sometimes, it seems.
                              Last edited by Curt_B; 11-05-2013, 05:39 PM.

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                              • Re: Aerodynamic modifications

                                Originally posted by Curt_B View Post
                                There's a lot of shape, line, and contour changes on PM's. Maybe comparable to Voodoo/Strega dragwise. Voodoo/Strega is an unnecessary boundary layer growth deal, PM's is a fluctuating pressure gradient deal due to the shape changes toying with the pressure drag. Strega's new canopy/windshield interface with the forward and aft facing, chamfered(?), step right at the minimum pressure location is undesirable at 500mph. Also, Strega's new canopy seems to transition to the turtle deck at an angle on the side view, which is less desirable than a nice straight line if that's what it had before. Considering the circumstances though, it's a mighty fine job.

                                Observation. Not trying to piss anybody off, lol, though I have done that before - inadvertently of course - sometimes, it seems.
                                Interesting... Last question I promise! -With Sea Furys, the common turtle deck seems to be the one 232 sports, versus one that blends to the tail like Furias's original one; since new Furias featured the 232 deck. Is there more drag introduced with a deck that ends well before the tail like on 232, versus Dago's deck?

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